Organic materials are of interest as ion battery cathode materials because they offer advantages over inorganic cathodes such as abundant resources and a low ecological footprint. However, they suffer from slow kinetics and a comparatively low potential. In this paper, we have investigated alkali induced changes in the electronic structure of tetracyanoquinodimethane (TCNQ) to be used as cathode material in Li-ion batteries. Lithium was inserted stepwise into TCNQ thin films by exposure to lithium vapour and analysis by photoemission (PES) was performed. The evolution of core levels, electronic structure and Fermi-level with increasing lithium insertion into TCNQ was monitored. The results show that lithium insertion takes place under integer charge transfer and polaron formation. We find no indication of deterioration of the material. The consequences of evolution of electronic structure and polaron formation for electrode potential and kinetic properties of the material are discussed.

In this contribution, we investigate the insertion of sodium into tetracyanoquinodimethane (TCNQ) and its effect on the electronic structure by means of a surface science experiment. We exposed a TCNQ thin film stepwise to sodium vapour and monitored the electronic structure by X-ray photoelectron spectroscopy (XPS) and ultra-violet photoelectron spectroscopy (UPS). During the insertion experiment three stages were observed, which can be related to three different phases, predominantly consisting of TCNQ(0), TCNQ(1-) and TCNQ(2-). With increasing sodium content the Fermi level shifts upwards and new electronic states appear in the band gap. For phases with high sodium content the sodium diffusion seems to be inhibited which we attribute to closed diffusion pathways in the molecular structure of TCNQ(1-).

Photoelectron emission spectroscopy and positron annihilation spectroscopy allow a comprehensive interpretation of the performance of IZO-based TFTs.